WASHINGTON - Contamination concerns led the U.S. Food and Drug Administration to delay expanding approval of the nasal flu vaccine FluMist to very young children.

The Washington Post reported Wednesday that the FDA had sent a warning letter about the delay following reports of contamination at a U.K. manufacturer of the drug.

The report said, however, the final FluMist product wasn't affected and the maker, MedImmune, Inc., expected to make the vaccine available for this year's flu season. The drug is approved for people aged 5-49. MedImmune was seeking to have the age range expanded to cover children as young as 1.

Officials from MedImmune told the Post that an unrelated pair of lawsuits filed by company shareholders is without merit. The lawsuits are aimed at blocking the proposed $15.6 billion deal that would sell the company to the British pharmaceutical firm AstraZeneca.